The invention relates to a method of charging a coolant into a cooling system via a conduit, such as a hose, to which the coolant is applied at the inlet end, and which is connected with the cooling system at the outlet end, and wherein the charging is controlled by a meter on the inlet end of the hose which controls a valve at the outlet end of the hose, a device therefor and use thereof.
Such a method takes place in connection with service and repair of cooling systems.
When a gaseous coolant is used, special physical conditions are involved, and thereby conditions which have to be taken into consideration when a given amount of gaseous coolant has to be charged.
Known methods concern charging by weight, which means that the charged amount is weighed during the charging.
Examples of such a charging are known from JP 8 303 960 A and U.S. Pat. No. 4,470,265 A, both of which describe charging by weight of the coolant.
Charging based on the measurement of the mass flow of the coolant is known U.S. Pat. No. 5,231,841 A. A constant volumetric flow is maintained by means of a flow valve. By measuring the pressure and the temperature the density may be determined after the valve, following which the mass flow may be calculated.
A similar method is known U.S. Pat. No. 5,758,506 A. Here, too, the mass flow is measured. By using a fixed resistance in the form of a nozzle and by measuring the pressure difference across the nozzle and measuring temperature and pressure before and after the nozzle, the flow through the nozzle—and thereby the charging—may be calculated.
These charging methods, however, suffer from a considerable inaccuracy, which is caused by the fact that the charging takes place via a hose whose interior volume depends on its length, which may be up to 7 meters, as well as its internal diameter, just as the supply pressure of the coolant, its temperature and the temperature of the surroundings have an effect on the density of the coolant. This is measured in weight per unit of volume.
Thus, the measured and calculated amount of coolant is just a measure of the amount which passes through the meter. However, this amount is not the amount which passes the charging valve at the outlet side of the hose because of the length of the hose between the measurements and the valve. This means inaccuracy of the charged amount of coolant.
To this should be added that the pressure may drop through the hose, as it will normally be higher at the inlet end than at the outlet end, and, thereby, that its density is higher at the inlet end than at the outlet end during the charging.
This means that the average density of the coolant in the hose will be smaller, and, thereby, that the amount in the hose will have dropped relative to an amount at the inlet side in the hose. Thus, the hose has been emptied to a certain degree from start to end of the charging, which amount will have been added to the cooling system without the meter having recorded it.
This difference in density will moreover be dependent on the length of the hose and its internal diameter, which, however, are variables which may be included in the necessary calculation of the compensation.
These factors contribute to making it difficult to charge the correct and precise amount of coolant into a cooling system.